1. Field of the Invention
The present invention relates to a diamond coated sintered body and in more detail it relates to a diamond coated sintered body which comprises a sintered body which is a ceramic based super hard sintered body comprising specific components and a diamond film superior in adhesion provided on the surface of the sintered body.
2. Description of the Related Art
Super hard alloy, sintered diamond, single crystal diamond and the like have been used for tools required to have high hardness and wear resistance such as cutting tools, abrading tools, die, and the like.
Among them, diamond tools are especially preferred because of their excellent hardness and wear resistance.
Hitherto, as the diamond tools, there have been used those which comprise a body made of a super hard alloy or high hardness metal on which a sintered diamond or single crystal diamond is mounted by brazing and other methods.
On the other hand, recently, production of diamond coated body has been studied which comprises forming a diamond film by deposition on the surface of a body of super hard alloy or high hardness metal using gas phase diamond synthesis techniques such as CVD method and PVD method and attempt has been made to apply the resulting diamond coated body to the above-mentioned uses.
Since diamond is the hardest substance, it is considered that diamond film formed on the surface of body of super hard alloy and the like can be effectively utilized as a coating material for imparting high hardness or wear resistance to the body or as a protective film for the body. For example, when a diamond film is formed on the surface of body made of super hard alloy used for super hard tools such as cutting tool and abrading tool, further excellent super hard tools should be obtained.
However, adhesion between the surface of super hard alloy and diamond is normally poor and practically usable tools have not yet been obtained.
Therefore, in order to improve adhesion between the surface of super hard alloy and diamond, it has been proposed to form an intermediate layer between the super hard alloy and diamond.
For example, Japanese Patent Kokai No. 58-126972 discloses a super hard alloy with a diamond film which is obtained by firstly forming an intermediate layer comprising at least one selected from carbide, nitride, boride and oxide of a metal of Group IVa, Va or VIa on the surface of a super hard alloy and then forming a diamond film on the intermediate layer.
However, such method as disclosed in the above patent publication employs stepwise film forming method which comprises formation of the intermediate layer and then formation of the diamond film and so this method is troublesome in production steps and besides, although improvement of adhesion is aimed at, the adhesion between super hard alloy and diamond film has not been sufficiently improved to practical level.
There has also been proposed a technique to improve adhesion between the surface of body comprising super hard alloy and diamond without providing an intermediate layer therebetween.
For example, Japanese Patent Kokai No. 63-100182 discloses a super hard alloy with diamond film prepared by forming a diamond film on a tungsten carbide super hard alloy containing a specific amount of Co and comprising tungsten carbide of a specific particle diameter.
However, this product also cannot be said to have sufficiently practical adhesion between super hard alloy and diamond film.
Especially, with increase in the amount of Co added, the thermal expansion coefficient increases and besides diffusion of carbon into Co occurs. As a result, formation of good diamond film becomes difficult and adhesion is also deteriorated and sufficient endurance cannot be attained.
Furthermore, Japanese Patent Kokoku No. 60-59086 discloses a cutting tool made by coating a diamond film 0.5-50.mu. thick on the surface of a ceramic body comprising Si.sub.3 N.sub.4 and/or SiC, However, cutting performance is not sufficient.
As the other example, Japanese Patent Kokai No. 1-201476 discloses a method of producing a sintered hard alloy having a diamond film, characterized by bringing a gas obtained by activating a raw material gas containing 2-30 mol % of carbon monoxide and hydrogen gas into contact with the sintered hard alloy and Japanese Patent Kokai No. 1-275759 discloses a sintered hard alloy with a diamond thin film, characterized by comprising a sintered hard alloy, an intermediate layer formed by bringing a gas obtained by exciting a raw material gas containing a carbon source gas in a concentration of at least 2 mol % therein into contact with a layer made on said sintered hard alloy, of at least one metal selected from the group consisting of Groups IVa, Va and VIa metals and Si and having a thickness in the range of 0.05-1 .mu.m, and a diamond thin film formed on said intermediate layer and having a thickness of 0.2-100 .mu.m.